What is XCMG XE750D Fault Code 2535-5 SPN1073 FMI5?

Fault Code 2535-5 (SPN1073 FMI5) indicates an Engine Coolant Temperature (ECT) sensor circuit has detected a current below normal or an open circuit condition. This J1939 diagnostic trouble code specifically points to the Engine Coolant Temperature sensor failing to provide proper electrical current feedback to the Engine Control Module (ECM).

On the XCMG XE750D excavator, this code directly affects the engine's ability to manage fuel injection timing, idle speed, and cooling fan engagement. The ECT sensor provides critical temperature data that the ECM uses to optimize combustion efficiency and prevent overheating. In used excavators operating in demanding conditions, this sensor circuit is particularly vulnerable to corrosion, vibration damage, and connector degradation—all of which can trigger this specific FMI5 (current below normal) fault.

Common Symptoms

When fault code 2535-5 is active on your XE750D, you may experience:

• Check Engine Light or malfunction indicator lamp illuminated on the dashboard
• Hard starting or extended cranking, especially during cold starts when ECM relies heavily on coolant temperature data
• Rough idle or erratic engine RPM as the ECM defaults to limp-mode fuel maps
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Reduced engine power or derate mode activation to protect the engine from potential thermal damage

Potential Causes

The most common technical reasons for this fault code on used XCMG excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire chafing against frame components near the engine block
• Corroded or loose connector pins at the ECT sensor plug—extremely common in machines exposed to muddy or wet job sites
• Failed ECT sensor with internal circuit breakage (resistance reading infinite/open)
• Damaged ECM connector terminals at pin locations corresponding to ECT signal and ground circuits
• Broken or frayed wiring between the sensor and ECM, particularly at harness flex points near engine mounts

How to Troubleshoot and Fix Code 2535-5 SPN1073 FMI5

Step 1: Visual Inspection Begin by locating the Engine Coolant Temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, bent pins, moisture intrusion, or physical damage. On used excavators, pay special attention to harness routing—look for wire insulation wear where the harness contacts metal surfaces.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. A functioning ECT sensor typically reads 2,000-3,000 ohms at room temperature (consult XCMG specifications). An open circuit (infinite resistance) confirms sensor failure. Also check continuity from sensor connector pins back to the ECM to identify wiring breaks.

Step 3: Circuit Voltage Check With the ignition on and sensor disconnected, measure supply voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. No voltage indicates an ECM supply circuit problem or blown fuse. Check ground circuit continuity to ensure proper sensor return path.

Step 4: Connector Service and Replacement Clean all connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Replace any damaged connector seals. If testing confirms sensor failure, install a genuine or OEM-equivalent ECT sensor and secure all harness routing with new zip ties away from heat and friction points.

Step 5: Clear Codes and Verify After repairs, use XCMG diagnostic software or a compatible J1939 scan tool to clear fault codes. Run the engine through warm-up cycles while monitoring live coolant temperature data to confirm proper sensor operation and code resolution.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the XCMG XE750D service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator electrical systems.